Jinyu, Ankoan, Murlocks, Kobyss, Naga, Gilgoblin…
Water people are such an eternal trope that they might even be more prevalent than elves. Yet we don’t have anything close to playable aquatic races. Hell, we even have two underwater zones, and had some underwater delves.
With Midnight coming, I’d strongly consider bringing Naga into the fold. Their connections to Elves and the Void, it’s almost necessary.
Naga are snake ppl, not fish ppl. But we need like 5 more fish races before one becomes playable.
The issue for Naga continues to be their appearance. They move on tails. They have no legs. So how do they sit on mounts?
This is what comes to mind when I think of that issue:
https://imgur.com/Hn6F3VF
There is something fishy about this post and I can’t put my finger on it.
Naga wouldn’t be riding a land horse. They would be riding a sea horse, so clearly, you’re wrong.
Ah so it would be a race that would only ever be able to ride one mount.
Attractive option! 
(Still trying envisage a Naga on a sea horse…na, not seeing it…)
Now you get to call me an idiot, because how in the world multiple Naga would ride a singular horse, land or otherwise?
Just make it so they can slither ultra-fast! I’d love to see that
Sure. In the air too?
Worgen have the ability to run fast. How many times have I actually used that on my Worgen. Hmm, do I need to take off my shoes to count the number? 
They’ll get a Visage form
Air is a fluid too.
And like Worgens who also have a run fast ability, its niche and hardly ever gets used.
If you were from a certain hillbilly junction near and dear to my gene pool, you wouldn’t be able to count all that far even if you took your shoes off.
+10 points if their visage form is Murloc
I’m a maths jeeniuz. I can do algerbra with my ears.
Yeah, the “no legs” issue is pretty much the thing that lingers for adding races. Or too many legs in the case of nerubian suggestions. I’m not sure what they could really do to make that work other than restrict mounts to ones like the “ride on a platform” set.
That video of someone tossing a brick into a drier comes to mind.
People whined about Drac’thyr armor. Now want another race with the same problem.
Or give them a body transformation option. Visage has been created for some races but it hardly ever gets used since the races are expected to be in their natural form for combat. If they provided a visage that made them into a more humanoid shape for things like riding that would be about the only way to do it.
Since they don’t have that now it would have to be provided with some type of lore or story reasoning for it to exist. Who knows, maybe Azshara agrees to do something to them to better blend in with the landbased Azerothian races.
PS: Azshara and the Naga were once Night Elves, I believe. So their humanoid appearance could be a nice blending of Naga scales and colouring on a Night Elf physical structure.
I do mental calculus every day and it has nothing to do with maths.